Many common medications interact with the caffeine you consume and cause harmful side effects. Some drugs slow the body's disposal of caffeine. These can result in insomnia, irritability, nervousness or heart palpitations when combined with caffeine.

• Birth-control pills

• Ciprofloxacin ( Cipro ) - prescribed for bacterial infections

• Cimetidine ( Tagamet ) - prescribed for ulcers

Drugs that stimulate the nervous system can also cause insomnia, anxiety or palpitations when combined with caffeine.

• Appetite suppressants ( Acutrim, Dexatrim )

• Theophylline ( Slo-Phyllin, Theo-Dur ) - prescribed for asthma

• Oral decongestants ( Contac, Propagest )

Caffeine can interfere with the sedative effects of the benzodiazepine tranquilizers ( Halcion, Valium, Xanax ). Perhaps most dangerous of all, when combined with the antidepressant monoamine oxidase (MAO) inhibitors ( Nardil, Parnate ), caffeine can lead to extremely high blood pressure or abnormal heart rhythms.